提升含氮基團電致色變元件之性能

Abstract

本論文使用多種以氮原子為變色基團之電致色變材料作為基礎，藉由不同的元件設計與搭配，來提升各種電致色變元件之表現。本論文主要針對有機以及有機無機複合電致色變材料進行性能提升之研究，因為這些材料相較於無機材料具有較多樣的顏色變化，且其材料特性可經由分子結構的設計做有效控制其電致色變的性能，而在這些電致色變材料中，又以氮原子作為變色機團之電致色變材料屬於最大宗，此外，這些以氮原子為變色基團之材料通常能夠提供較短波長光波範圍的吸收，並且由於氮原子本身電子雲密度較高的特性，讓該類材料相較於他者有更低的氧化電位。這些特性，使得氮原子為基礎變色基團材料成為本論文之主軸。 論文首先探討三苯胺為主要變色基團的樹枝狀導電高分子作為變色材料，該高分子本身就具有高光學穿透度對比之優勢，為使其變色表現能充分發揮，本研究合成出普魯士藍類似物之奈米顆粒，該顆粒能夠提供極佳的離子儲存能力並且展現出高穿透度的特性，係理想的對電極材料。所獲致之元件展現出低操作電位窗(-0.4 ~ 0.1 V)與高穩定性的特殊優勢。再者，由於三苯胺衍生物之樹枝狀高分子具有短波長光波吸收特性，恰好能夠跟PEDOT (Poly(3,4-ethylenedioxythiophene))作完美的組合，獲致出具有全波段光譜吸收特性之元件。 本論文亦針對紫精系列變色分子作探討。紫精系列變色分子的研究由來已久，其高光學穿透度對比一直是其特色之一，然該分子在元件操作中一直存在有分子聚集、老化等現象，不利元件的表現。本論文著重在苯基紫精(Phenyl viologen, PV)為基礎之元件表現上做改進，因該分子具有較低的操作電位。首先，本研究合成出具有含穩定自由基的陰離子作為搭配PV的陰離子，形成一紫精-自由基鹽類(Viologen radical salt, VRS)，由於該自由基陰離子能夠有效作為兩極材料間的中間體(Mediator)，防止操作中的PV分子團聚，最終獲致的元件具有相當良好的操作穩定性，同時表現出極低的需求操作電位。提升元件操作穩定度的另一策略則是在PV的元件系統中預先加入熱聚合網狀高分子的前驅物，隨後施以熱處理，如此可得一電致色變凝膠。該凝膠在元件中操作時，熱聚合而成的網狀高分子能防止PV的團聚，因而使得元件穩定性的大幅提升。之後，本研究亦開發出雙功能的乙烯基芐基紫精(Vinylbenyl viologen)。該分子能同時具有變色與作為交聯劑的功能，除簡化生產步驟外，亦提供有別於PV的可見光吸收特性。而最終，藉由控制VBV與PV在元件中的濃度，可以得一具有高穩定性、低操作電壓，且全波段可見光譜吸收的電致色變元件。 在論文的最後，亦針對新類型金屬超分子高分子電致色變材料作探討。在該類型材料中，鈷離子為基礎之金屬超分子高分子(polyCo)具有透明至黑色的變色潛力，然該高分子透明態因反應速率極慢，使其透明態一直難以展現。本研究藉由適當氧化還原對的加入，首次成功使polyCo展現出透明至黑色的可逆變色特性，並同時表現出良好的操作穩定性。

In this dissertation, several nitrogen-based electrochromes were studied. In the beginning of this dissertation, triphenylamine-based dendritic polymer was investigated. Since this material itself demonstrates significant color contrast, favorable electrochromic performance can be obtained without the assistance of complementary materials. To enable its desirable electrochromic property to be fully presented, Prussian blue analogue nanoparticles were synthesized and served as the counter material. In addition to significant color contrast, the resulted electrochromic device (ECD) demonstrates excellent cycling stability while presenting very narrow operating potential window of -0.4 ~ 0.1 V. Since the mentioned triphenylamine-based dendritic polymer absorbed light at short-wavelength region while giving anodically coloring characteristic, it perfectly complements the property possessed by PEDOT, which gives cathodically coloring feature while show light attenuation mainly at long-wavelength region. As the result, ECDs with panchromatic feature can be achieved when it was work in conjunction with poly(3,4-ethylenedioxythiophene) (PEDOT). The viologens were also studied in this dissertation. Even though the viologens were well-known for their high color contrast, their lack of cycling stability resulted from aggregation or aging process remains. Studies in this dissertation were focus on phenyl viologen (PV) because of its relatively low-driving voltage comparing to other viologens. Initially, a novel compound named viologen radical salt (VRS), which composed of PV dication and two (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl derivative (TEMPOD) anions, was synthesized. Because TEMPOD redox couple can serve effectively as a mediator between two electrochromes in the ECD, the aggregation of PV can be hindered, resulting in better cycling stability. Meanwhile, the low-driving voltage of PV was inherited in this VRS-based ECD. Another strategy to lengthen its cycling life is to incorporate thermally initiated cross-linked polymer network into ECDs. The polymer matrix in the obtained electrochromic gel effectively prevents formation of PV agglomeration, giving better cycling stability. Following this, a dual functional vinylbenyl viologen (VBV) compound, which serves as a cross-linker and an electrochrome simultaneously, was synthesized. Ultimately, ECDs composed of PV and VBV demonstrates high stability, low-driving voltage, and panchromatic feature while requiring easier fabrication process. In the last part of this dissertation, a novel cobalt-based metallo-supramolecular (polyCo) was utilized as electrochromic material. Even though polyCo itself demonstrate black-to-transmissive color changing potential, its transmissive state is hard to be obtained due to its sluggish electrochemical reaction. Herein, through the addition of suitable redox couple, polyCo was able to demonstrate black-to-transmissive property with good reversibility.